End point moisture content control for sand



Sept. 19, 1961 H. w. DIETERT EI'AL 3,000,064

END POINT MOISTURE CONTENT CONTROL F OR SAND Filed July 11, 1957 2 Sheets-Sheet l HARRY W. DIETERT RANDOLH L.D|ETERT ATTORN Sept. 19, 1961 3,000,064

H. W. DIETERT ETAL END POINT MOISTURE CONTENT CONTROL FOR SAND 2 Sheets-Sheet 2 Filed July 11, 1957 ATTORNE 8 United States Patent 3,000,064 END POINT MOISTURE CONTENT CONTROL FOR SAND Harry W. Dietert and Randolph L. Dietert, Detroit, Micln, assignors to Harry W. Dietert Co., Detroit, Mich, a corporation of Michigan Filed July 11, 1957, Ser. No. 671,221 23 Claims. (Cl. 22-89) The present invention relates to end point moisture content control for sand.

It is an object of the present invention to provide an automatic system for adding water to sand in a mill, mixing the sand and water, sensing the moisture content of the sand, and preventing termination of the addition of water which might result from sensing of a moist sample of sand in the mill while the average moisture content is below that required.

More specifically, it is an object of the present invention to provide a system for adding water to sand in a mill, the system including a moisture sensitive element adapted to measure moisture content of sand at a particular point in the mill, and including means for preventing accidental termination of addition of water which might result from passage of a small volume of moist sand across the moisture sensing element.

Still more specifically, it is an object of the present irrvention to provide apparatus for sensing moisture content of sand in the mill as water is added thereto, means for continuing the addition of water until the moisture content reaches a predetermined fraction of the required final moisture content, means for reducing the rate of flow of water into the mill until a second higher value of moisture content is sensed, and means for thereafter repeatedly sensing moisture content at intervals to provide for addition of Water if any of the subsequent moisture sensing operations results in a sensing of less than required moisture content.

It is a further object of the present invention to provide end point control for sand moisture in a mill including a moisture probe located in a wall of the mill, mixing members in the mill movable over the moisture probe and adapted to compact a specimen of sand against the probe, a scraper movable over the probe following each compacting operation effective to remove compacted sand from the surface of the probe, said probe including a metal button having a surface exposed at a surface of the wall of the mill, and a surrounding bushing formed of tetrafluoroethylene under the trade name Teflon.

It is a further object of the present invention to provide a moisture probe comprising a tube terminating at one end in a conical seat, an annular bushing received in said one end of said tube and having an outwardly enlarged internally and externally conical portion engaged in said seat, a probe button formed of metal received in said bushing having an outwardly enlarged conical end portion seated in the internal conical portion of said bushing.

It is a further object of the present invention to provide a probe of the character described in the preceding paragraph including resilient means for urging said probe button firmly against the seat in said bushing.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention, wherein:

FIGURE 1 is a combined schematic view and wiring diagram of the end point moisture content control for sand.

FIGURE 2 is a longitudinal sectional view through the moisture probe.

FIGURE 3 is a longitudinal section through the thimble element of the probe.

Referring now to the drawings, the sand mill 10 is adapted to receive sand from a plurality of hoppers 12 and water is added to the sand through valve means later to be described, but the addition directly to the mill is through sprinklers 14 connected to a receptacle 16 which receives water from a discharge pipe 18. The sprinklers 14 are suitably supported as for example by a part 20, for roation with the rollers 22.

In FIGURE 1, which is diagrammatic in character, the sprinkler heads are shown as located above the rollers 22 but in practice they are preferably circumferentially spaced therefrom.

The sand mill 10 is of the type including the relatively heavy rollers 22 previously referred to and in addition and rotatable therewith, there is provided a plow 24 having a leading edge spaced only slightly above the bottom wall of the mill and adapted to scrape the sand therefrom after it has been compacted by the rollers 22. In practice the leading edge of the plow 24 may be spaced slightly upwardly from the bottom Wall of the mill, as for example approximately A of an inch.

Located in the bottom wall of the mill it) is a moisture probe 26, details of which will be presently described. The moisture probe is preferably located directly under the path of the rollers 22 so that as the rollers pass over the moisture probe, they compact the sand against the moisture probe to give a reading the value of which is determined simultaneously by the moisture content of the sand and its state of compression.

Due to the specific nature of the moisture probe, the succeeding passage of the plow 24 thereover is effective 'to remove all sand previously compacted against the face of the probe. The moisture probe is adapted to sense a capacity which is dependent on the moisture content of the sand. In addition, means are provided for measuring the temperature of the sand in the mill. This means, illustrated as comprising a thermocouple 38 connected to a potentiometer 40 including the converter 40a, input transformer 40b, voltage amplifier 4ilc, and power amplifier 40d is adapted to rotate a motor 42 connected to the movable arm 44 of a rheostat and to a cam 46. Dependent on the voltage applied by the thermocouple, the motor 42 rotates to move the arm 44 of the rheostat to the required position to balance the temperature signal. The corresponding rotation of the cam 46 efiects adjustment of an adjustable capacitor 48.

The moisture probe 26 is connected by lines 50 and 52 to a moisture measuring bridge indicated at 53, which is a measuring instrument identified as Tektor Unit #101, manufactured and sold by the Fielden Instrument Division of the Robertshaw-Fulton Controls Company. The line 50 is grounded as indicated at 54, and line 52 is connected through a high capacity capacitor 56 to instrument connector X. Also connected in line 52 is a variable trim capacitor 58 efiective to make the required adjustments in the unit. The variable capacitor 48, actuated in accordance with the temperature of the mixture in the mill is connected to the instrument connection X and to a second instrument connection Y. The instrument connection X is connected to the grid of a vacuum tube, for example a 6SN7 tube, connected as shown to have its output applied to a relay coil M which actuates switch contact arms M1 and M2. Also connected to the instrument connections are an adjustable first point capacitor 62 and an adjustable end point capacitor 64. The end point capacitor 64 is connected in parallel with a high capacity, as for example 2000 M.M.F., fixed capacitor 66, by normally closed contacts R7a of a relay R7 later to be described.

Described in general terms, the system operates as rollers 22 pass over the sand probe.

follows: The operator pushes a button which starts rotation of the mixing apparatus, the sand being dumped in at this time or subsequently. Inasmuch as sand may be rurnped-in from one of a plurality of hoppers, it is desirable to effect substantial mixing of the sand before any attempt is made to determine its moisture.

After a predetermined interval of mixing, operation of the moisture control device is initiated. A timer is started which will insure rechecking the moisture con- 'tent after a predetermined interval even though the instrument may previously have indicated sufficient moisture. This is because of the possibility of a false reading and rechecking after a predetermined interval will insure continued operation of the instrument until the moisture content is adequate.

' During operation of the instrument, the first point valve Va an dthe end point valve Vb are opened and water is supplied to the sand while it continues to be mixed. Inasmuch as the mixing operation comprises the passing of the rollers 22 over the moisture probe 26, followed almost immediately by passage of the plow 24, it will be appreciated that even when the sand reaches the required moisture content, this correct moisture content will be indicated only at intervals determined by the passage of the rollers 22 over the probe. After the scraper or plow 24 has passed over the probe, the sensing system will indicate a moisture deficiency until the succeeding sample of moist sand is compressed against the probe.

At this time it is desired to add the water rapidly to bring the moisture content approximately up to but definitely below the desired value. Accordingly, at this time control of the instrument is by the first point capacitor 62 and temperature compensating capacitor 43. Eventually, the instrument senses the proper moisture content for a brief interval and the system is arranged at this time to close the large capacity first point valve Va and to shift control of the instrument to the combination of the three capacitances, the end point capacitance 64, the temperature compensating capacitance 48, and the modifying capacitance 66. Capacitance 66 is a large value capacity, for example 2000 micro-micro-farads, which is suflicient to stop the 6SN7 tube from conducting and in turn deenergize relay M and causing M2b to make contact at M2c which completes the circuit to contacts RSa to energize relays R7 and R4, thus taking capacitance 66 out of the circuit at contacts R7a for the remaining part of the cycle, leaving the control of the instrument to the sum of the end point capacitance 64 and temperature compensating capacitance 48. Thereafter, water continues to be added to the mill at a reduced rate by the end point valve Vb until the first indication of the ultimate desired moisture is obtained. It is recognized however, that this may be a false indication resulting from sensing the moisture content of a small specimen not indicative of the true average moisture content of the sand. Accordingly, means are pro- :vided at this time to close the end point valve while the mixing of the sand continues. During the following interval moisture readings are taken periodically as the So long as these moisture readings all indicate sufiicient moisture the valve Vb remains closed. A timing means is provided to operate over for example three seconds, which prevents opening of the end point valve during the brief intervals between successive sensing operations. For example, resensing may occur every two seconds and the timer may be set to time out in three seconds. At the end of two seconds if the sensing of moisture indicates sutn'cient -moisture, the timer is reset to zero.

On the other hand, if during this rechecking interval a moisture sensing operation indicates ins'ufi'icient moisture, the moisture valve opens and remains open until a second sensing of adequate moisture. This operation continues for an intervaldetermined. by.an additional timer which operates to terminate the rechecking operation and to maintain the end point valve Vb closed, thus ending the cycle.

When the system is set in operation, the capacities of the moisture probe 26, the trim capacitor 58, the temperature responsive capacitor 48, and the first point capacitor 62, are all connected to the instrument connections X, Y. When suificient moisture has been added to the mill 10 to increase the capacity of the moisture probe 26 to a different value, the 6SN7 tube will conduct and will energize the relay coil M.

Oscillation of the 6SN7 tube is dependent upon the algebraic sum of thecapacities connected to the instrument connections X and Y.

The addition of water through the discharge pipe 18 is through a first point valve Va which is air controlled and the supply of air controlling the valve is in turn con trolled by a winding Val which will subsequently be described. At the same'time' an end point valve Vb is provided also controlled by air, which in turn is controlled by solenoid Vbl. The arrangement is such that when the solenoids Val I and Vbl are energized the corresponding valves are closed. The valves of course are open when the respective windings are de-energized.

The operation of the complete system will be described in connection with the illustrated circuit, which will be described to the extent necessary to understand the system. A ll0-volt power line indicated at 70 is connected to the control circuit through a manual control switch 71. The control circuit includes the transformer Ta which is energized whenever the manual switch 71 is closed and which in turn supplies the primary of a second transformer Tb having the 250-volt, 6.3-volt secondary windings illustrated in the Tektor unit.

In operation sand is dumped into the mill from the hoppers 12 without regard to the moisture content of the sand in the hoppers. For example, the sand in one of the hoppers may be substantially moist and this sand may be dumped into the mill first so that it immediately contacts the moisture probe 26. The drier sand from the other hopper is at the top of the mill and is ineffec tive on the moisture probe. In order to insure that this condition does not prevent the required addition of moisture, the circuit includes timing means operable to pro vide a cycling of the control system after a predetermined interval irrespective of whether or not the instrument cut off the supply of water during the first timed interval. This means comprises a timer resistance Tl having a switch'arm Tla associated therewith. The switch arm Tla may for example be in the form of a bi-metallic contact member which is normally open and which closes after the resistance Tl has been energized for a substantial period, as for example 15 seconds. Closure of the manual switch 71 starts heating resistance element Tl through contact R211, the contact being in the illustrated position when the relay R2 is de-euergized.

After the predetermined initial period, as for example 15 seconds, has elapsed, the switch arm Tla closes energizing relay R2 and moving relay arm R2a to its lower position establishing a holding circuit through the relay R2 and de-energizing timer TI. The relay RZ-Iemains energized for the remainder of the complete cycle. In addition, energization of relay R2 shifts relay arm R2b to the left energizing relay R1. Energization of relay R1 shifts relay arm Rla to the left establishing a connection to the lower portion of the circuit through jumper line 80, around arm R2b, which remains to the left, holding relay R1 in. g

. During the interval measured by the timer Tl it may be possible for suflicient water to have been added to the sand and mixed therewith, in which case the opera tion should be terminated. In other cases a false signal portion of the system. When the switch arm R2b is in its lowermost or clockwise rotated position it energizes relay R1 which closes a circuit through switch arm R1a, thus reenergizing the lower portion of the circuit. The interval between energization of relay R2 and energization of relay R1 is substantial and all circuits completed through portions of the wiring diagram below relay R1 in the figure are de-energized so that all holding circuits drop out. When the switch arm Rla completes its movement all circuits are again reenergized and checking of the moisture of the sand is resumed. If in fact, the moisture content of the sand is sufiicient this recheck results in quick cycling of the instrument to close valves Va and Vb and they will remain closed for an interval determined by energization of a timer ES2 later to be described, which finally completes the cycle.

The operation of the system during the interval controlled by the timer TI is exactly the same as it would be if the timer were omitted. The function of the timer is to restart the complete cycle after a predetermined interval so that additional water can be added if the operation of the system was terminated as a result of a false signal during the first timed interval. A second important function of the initial timing period depends upon the following: It may happen that during the initial timing period a first signal is received from the moisture measuring unit which will have the effect of closing the large capacity valve Va and leaving additional water to be supplied through the relatively smaller end point valve Vb. If the false signal was the result of a small quantity of very moist sand happening to contact the moisture probe, a large volume of water may in fact be required to bring the average moisture content of the sand to the required value. During the initial interval timed by the timer Tl, water will be added through the small capacity valve Vb. However, when the timer Tl times out the control circuit is completely de-energiz ed and re-energized, thus starting afresh with the large capacity valve Va open and the valve will remain open until the measuring unit makes the first signal indicating adequate moisture, which signal is sometimes referred to herein as a wet signal.

Assuming that insufiicient water has been added to the sand, the rollers and plows continue to rotate, and water is now added to the mill through the valves Va and Vb. The solenoid Val of the first water valve Va is energized through lines 72, 74, 76, selector switch SS1, switch arm R311, switch arm Rla, and jumper 80. 'En ergization of the solenoids Val maintains the first point valve Va in open condition. In like manner, the end point valve Vb and its solenoid Vbl are energized through lines 72, 74, 78, selector switch SS2, switch arm RSb, ,switch arm ESla, switch arm Rla, and jumper 80. The addition of water and mixing of the sand continues concurrently until the moisture content of the sand approaches a value near to but definitely below the final required value. At this time the value of the capacitance of the moist sand as sensed by the moisture probe 26 such that the various capacitances connected to the points X, Y, including the first point capacitance 62', operate to cause the 6SN7 tube to oscillate, thereby establishing a current through the relay coil M sufiicient to shift the contacts M1 and M2 to the left from. the posi- .tion shown.

Closure of the switch M1 establishes a current through relay R3, switch arm Rla, and jumper 80. Energization of relay R3 moves switch arms R3a downwardly from the illustrated position, thus breaking the circuit through the solenoid Val and closing the first point valve .Va. Switch arm R3a completes a circuit through the relay R3 and through the solenoid 82 of a switch having contacts indicated generally at 82a. Energization of solenoid 82 moves switch contacts 82a upwardly, thus disconnecting the first point capacitance 62 and connecting the end point capacitance 64 and the bias capacitance 66 into the circuit. It will be observed that thecireuit through relay R3 is held closed by the switch arm Rita and hence from this time to the end of the cycle, relays R1, R2 and R3 remain closed.

In addition to the foregoing, energization of the relay R3 shifts the switch arm R3b downwardly, thus preparing a circuit for subsequent energization of relay R5. This circuit extends from the switch arm R4b to contact M211, contact M2b, switch arm R3b, switch arm Rla, and jumper 80.

Since this first indication of adequate moisture was based upon control of the first point capacitance 62 and the temperature compensating capacitance 48, subsequent passages of the rollers over the moisture probe will not result in indications of adequate moisture until a substantial additional quantity of water has been added. Ordinarily, it is preferred to add approximately of the water while the first point valve Va remains open, the adidtional 20% being added at a much slower rat through the smaller end point valve Vb.

As soon as the scraper has removedthe moist sand from the moisture probe following this first indication, relay coil M is de-energized and contacts M1 and M2 again return to the illustrated position to the right. At this time a circuit is completed to relay R4 through the normally closed switch arm RSa, contact M20, contact M2b, switch arm R3b, switch arm Rla, and jumper 80.

Energization of the relay R4 closes switch R4a estab lishing a holding circuit for the relay R4 which keeps the relays R4 and R7 in throughout the balance of the cycle. Energization of the relay R7 opens normally closed contacts R711, thus disconnecting bias capacitance 66 from the circuit and leaving the end point capacitance 64 in control. The operations are continuous without further change until there is a second indication of adequate moisture which as before, energizes the relay coil M and shifts the contacts M1 and M2 to the left. The contact M1 has no further function since it has already energized relay R3 which remains energized through a holding circuit for the balance of the cycle, However, movement of the switch arm M2 to connect contacts M211 and M2b energizes relay R5 through switch arm R tb, contacts M2a, M2b, switch arm R3b, switch arm Rla, and jumper'80. Energization of the relay R5 shifts switch arm R5b to the lower position, thus breaking the circuit to solenoid Vbl and closing the end point valve Vb. This would normally constitute the end of the cycle but additional provision is made for recheoking the moisture content a number of times to insure against premature termination of the cycle while the average moisture content of the sand is below that required. 1

The brief interval in which the switch arms M1 and M2 are to the left (before the next succeeding passage of the plow 24) has closed the end point valve 'Vb, but downward movement of the switch arm R5b has established a holding circuit through the relay R5which in cludes switch arm ESla of a short interval timer BS1. Thus, as long as the switch arm ESla remains closed, the relay R5 will remain energized and the end point valve Vb will remain closed. The motor of the timer ESl'is at this time energized through switch arm RSa, contacts M20 and M2b, switch arm R3b, switch arm Rla, and jumper 80. The timer ESl may be set for an interval for example of three seconds and after three seconds the switch arm ESla will open if the timer is permitted to run its course. However, during the three seconds in which the timer B81 is timing out, there will be a sub sequent sensing of moisture content and if the moisture content of the sand is adequate relay M is momentarily energized and switch arm M2 will interconnect contacts M2a and M2b briefly and then return to interconnect contacts M2b and M2c. This will have the effect of break ing the circuit to the motor of timer ES1 at the contact M20 and return of the switch arm M2 to the contact M2c will restart the timer for timing out the same intertion of the thimble with clearance.

val. Thus, so long as the periodic moisture'sensing operations sense adequate moisture, the timer will be auto matically restarted so that the timer contact arm ESla will never open and the relay R will remain energized through switch arm R5b, switch arm ESla, switch arm -R1a, and jumper 80. This will interrupt the circuit through solenoid Vbl at switch arm R5!) and the end point valve will remain closed. If however, passage of a roller 22 over the moisture probe gives a dry signal, there will be sufiicient time for the timer ESl to time out, causing opening of timer switch arm E8101 and breaking the circuit to the relay R5, thus restoring switch arm -R5b toits illustrated position. This will complete the circuit through the solenoid Vbl and reopen end point valve. Vb. The end point valve Vb will remain open until a subsequent sensing of moisture content indicates the correct value thereof at which time the end point ,controlyalve will close and rechecking will resume. The timer motorESl is restarted and switch arm ESla closed when relay R5 is next energized, by the next wet signal.

In order to terminate the cycle after a predetermined interval which may be devoted to rechecking, a longer interval timer BS2 is provided having contacts ES2a in a branch circuit connecting the relay R5 across the lines. Thus, when the switch arm ESZa is closed, the relay R5 remains energized, switch arm RSb remains in its lower position, thus interrupting the circuit to the solenoid Vbl, and finally terminating the cycle.

Initiation of the longer interval timer which finally terminates the cycle is initiated through normally closed switch arm R6a, relay R8, switch arm R511, contact M20, contact M2b, switch arm R312, switch arm Rla, and jumper 80. Energization of relay R8 closes switch arm R8a, thus energizing relay R6 which in turn closes switch R6b, establishing a holding circuit through relay R6 and opening switch arm R6a. The continued energization of relay R6 and closure of switch arm R6b maintains the motor of timer ES2 energized for a predetermined interval upon the termination of which, timing out of the timer closes switch arm ES2a, thus establishing a circuit through relay R5 and moving switch arm RSb downwardly from the illustrated position to break the circuit to solenoid Vbl. This finally closes the end point control valve Vb if it was open at this time and marks the end of the cycle.

Referring now to FIGURE 2, the moisture probe is adapted to be mounted in the bottom wall 100 of the tank or mill 10. More specifically, the bottom wall 100 of the mill is provided with removable wear plates 102 and one of these is recessed as indicated at 104 to receive a flat cup-shaped element 106 which receives a fiat plate 108 of a suitable di-electric plastic material, preferably tetrafiuoroethylene sold under the trade name Teflon. The plate 108 of plastic material is retained in the cup 106 by means of rivets 110 having relatively large cylindrical heads 112. Centrally, the plate 108 is provided .with a circular opening 114 which receives an assembly comprising a metallic thimble 116, details of which are :best seen in FIGURE 3. The thimble 116 includes a cylindrical wall 118 which is relatively thin, a conical wall portion 120, and a cylindrical recess 122 the side Walls of which are provided with openings 124 for the reception of a pin. The lower end of the thimble 116 .has a tapped opening 126.

In the assembly, a Teflon button 128 is provided which .is shaped to fit within the open end of the thimble 116 and itis retained therein by means of a pin extending through the openings 124 of the thimble and through the lower reduced portion of the button. Surrounding the metal thimble 116 is a plastic sleeve 130 having an upper cylindrical portion to receive the cylindrical portion of the thimble, a conical portion therebetween, and an enlarged cylindrical opening which receives the lower por- The outer edge of the sleeve liao fills the opening 114. The upper surfaces of the heads 112 of therivets, the plastic plate 108, the sleeve 114, the buttonl120, and the cylindrical portion 118 of the thimble are all coplanar and occupy the plane of the upper surface of the wear plate 102.

- Rigidly connected to the thimble is an elongated center post 132, its upper end having a reduced threaded extension received in the tapped hole 126 provided at the lower end of the thimble. In order to retain the assembly in its lowermost position, an abutment ring 134 is provided in a tube 136 the upper end of which is welded to the bottom wall of the cup 106. Above the ring 134 is an indented groove indicated at 137 which forms an abutment'against which the lower side of the ring 134 seats. Below the ring 134 is a plastic washer 138' having a downwardly extending reduced extension which-re; ceives a metallic abutment washer 140. The lower-end of the center post 132 is threaded as indicated at 142 and carries a nut 144 which through a washer 146 sup ports a plastic washer 148. The plastic washer 148'has a reduced upper extension receiving a brass washer 150. Extending between the metal washers and 150 and surrounding the center post is a compression spring 152. The spring urges the center post and hence the stainless steel thimble, the button and the sleeve downwardly and maintains them in accurately centered and seated relation against the respective conical supporting surfaces. The center post is provided with an elongated insulating sleeve 154 which prevents accidental engagement between the spring and the center post.

In order to maintain the metallic elements of the prob at a temperature at least as high as that of the sand within the mill, suitable electric heating means is associated with the structure, this means being diagram,- matically indicated at 156.

At its lower end the tube 136 is connected to an angular conduit which receives a coaxial cable diagrammatically indicated at 162. The lower end of the center post 132 is connected to the conductor of the coaxial cable through a resistor (164.

With the foregoing construction it will be observed that the space between'the exposed edge of the stainless steel thimble and the nearest adjacent grounded metallic elements is determined by the spacing of the closest rivets 110 to the thimble. When this space is bridged by a quantity of moist sand, the exact capacitance of the moist sand may be measured by the connection between the center post of the moisture probe and ground.

Inasmuch as the probe is exposed to sand in a mill which is subjected to a mixing action, the abrasive effect of the sand is to wear away the material exposed thereto. By employing cylindrical heads 112 on the rivets 110 and by forming the upper end of the thimble in the form of a cylindrical shell, it will be observed that a Wearing away of the surface of the elements of the moisture probe by the continued passage of sand thereover will not afliect the capacitance measurement dependent upon the moist sand surrounding the exposed end of the moisture probe.

It is desirable in the present probe to insure that a specimen of sand, having been compacted against the probe to give a reading of moisture content, may be removed in its entirety. by the next passage of a scraping element in proximity to the surface of the probe. This is accomplished by employing polytetrafiuoroethylene as the resin from which the'plate 108, button 128, and sleeve 130 are formed. Preferably, the plastic compound contains approximately 20% coke flour or graphite fill to produce surface characteristics facilitating separation of a compacted specimen of sand therefrom.

The drawings and the foregoing specification constitute a description of the improved end point moisture content control for sand in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims. 1 a

What we claim as our invention is:

1. Apparatus for tempering granular material which comprises a mixer for mixing granular material and water, means for adding water to the granular material including a shut-ofi valve, moisture responsive means for measuring the moisture of the granular material in the mixer during addition of water thereto and during mixing of the granular material and water therein, means responsive to attainment of the desired granular material moisture content in said mixer operatively connected to said valve to close said valve, and timing means operable after a predetermined short interval to retest the mixture in the mixer for moisture content and operable to resume the addition of water if required.

2. Apparatus for tempering granular material which comprises a mixer, mixing means in said mixer, means for adding water to the granular material in the mixer during continued operation of said mixing means comprising first point and end point water shut-off valves, testing means for testing the increasing moisture content of the granular material during continued mixing and Water addition, means responsive to determination by said testing means of a first moisture content lower than the required final moisture content to shut off said first point valve, means responsive to determination by said testing means of final required moisture content to shut ofi said end point valve, and timing means operable after a predetermined short interval to retest the moisture content of the mixture and operable to resume the addition of Water if required. 1

3. Apparatus for tempering granular material which comprises a mixer, mixing means in said mixer, means for adding water to the granular material in the mixer during continued operation of said mixing means comprising first point and end point water shut-off valves, testing means for testing the increasing moisture content of the granular material during continued mixing and water addition, means responsive to determination by said testing means of a first moisture content lower than the required final moisture content to shut off said first point valve and to reset said testing means for a higher value of granular material moisture content, means responsive to determination by said testing means of final required moisture content to shut ofi said end point valve, and timing means operable after a predetermined short interval to retest the moisture content of the mixture and operable to resume the addition of water if required.

4. Apparatus for tempering granular material which comprises a mixer, mixing means in said mixer, means for adding water to the granular material in the mixer during continued operation of said mixing means comprising first point and end point water shut-ofi valves, testing means for testing the increasing moisture content of the granular material during continued mixing and water addition, means responsive to determination by said testing means of a first moisture content lower than the required final moisture content to shut ofi said first point valve and to reset said testing means for a much lower valve of granular material moisture content to ensure operation of said first point valve, means operated automatically immediately thereafter to again reset said testing means to the final desired moisture content, and means responsive to determination by said testing means of final required moisture content to shut off said end point valve.

5. Apparatus for tempering granular material which comprises a mixer, mixing means in said mixer, means for adding water to the granular material in the mixer during continued operation of said mixing means comprising a water shut-E valve, test means for testing the moisture content of the granular material during continued mixing and water addition at short intervals, a timer started by the first sensing by said test means of adequate moisture, the period of said timer being somewhat longer than the interval between successive moisture tests, means for restarting said timer whenever'said test means determines adequate moisture, and means operated by said timer if a moisture test indicates insufiicient moisture to reopen said valve. 1

6. Apparatus for tempering granular material which comprises a mixer, mixing means in said mixer, means for adding water to the granular material in the mixer during continued operation of said mixing means comprising a water shut-ofi valve, test means for testing the moisture content of the granular material during continued mixing and water addition at short intervals, a timer started by the first sensing by said test means of adequate moisture, the period of said timer being somewhat longer than the interval between successive moisture tests, means for restarting said timer whenever said test means determines adequate moisture, and means operated by said timer if a moisture test indicates insuflicient moisture to reopen said valve, and additional timing means operable for a predetermined interval after initial starting of said first mentioned timer to close said valve and finally terminate the water addition cycle.

7. In a mill for mixing granular material and water, a moisture probe device comprising a flat plate structure in a wall of the mill comprising a plastic material containing polytetrafiuoroethylene as its resin constituent and having spaced metal elements exposed in its surface, means in the mill comprising a member movable overthe plate structure to compress moist granular materialz thereagainst, and means movable over the plate structure:

to push the compacted granular material off the platestructure, a ground connection to one of said elements. and an instrument connection to said other element.

8. Structure as defined in claim 7 in which said plastic material contains a substantial quantity of carbon select-v ed from coke fiour and graphite.

9. In a mill, a wear plate on the bottom wall thereof having an upwardly open shallow recess, a probe in said recess comprising a shalow metal cup, a plastic plate in said cup having a central opening and cylindrical heads ed rivets connecting said plate to the bottom Wall of said cup, a plastic sleeve in said opening having anupwardly open cylindrical portion and a lower conicalportion, a metal thimble in said sleeve having an upper cylindrical portion and a lower conical portion shaped to fit against the conical portion of said sleeve, a plastic: button in said sleeve, a metal rod connected to said thimble, a metal sleeve connected to said cup, and resili-' ent means in said metal sleeve acting between said rod and metal sleeve to urge said cup downwardly into firm engagement with the conical portion of said plastic sleeve.

10. A moisture probe device adapted to be mounted in the wall of a container for material Whose moisture is to be determined, said device comprising a shallow metal cup, plastic di-electric material received within said cup, metallic fastening elements extending through said plastic material into the material of said cup, said plastic material and said cup having centrally thereof registering openings, a generally tubular bushing of dielectric material received in both of said openings, said bushing having an enlarged outer portion, a reduced in? ner portion, and a conical portion interconnecting'said outer and inner portions, a metal thimble having an outer cylindrical portion shaped to fit snugly within the enlarged outer portion of the opening in said bushing and a conical portion at the inner end thereof, said device serving to determine electrical capacitance existing be-' tween the exposed edge of said thimble and the adjacent metallic fastening elements.

11. A probe device as defined in claim 10 comprising resilient means urging said thimble inwardly with respect to said bushing.

12. A probe device as defined in claim 10 comprising a metal tube extending rearwardly from the central opening in said cup, means fixedly securing said bushing in' said tube, a rod extending outwardly from the inner-end '11 of-said thimble, and resilient means extending between said rod and said bushing operable to bias said thimble outwardly to maintain it tightly 'on the conical portion of said bushing.

13. Apparatus for tempering granular material which comprises a mixer for mixing granular material and water, means for adding water to the granular material in the mixer including a shut-01f valve, said mixer including a roller movable in a circular path about a vertical axis concentric with the mixer and operating to compress specimens of moist granular material against the bottom wall of the mixer, a scraper movable in a circular path about a vertical axis concentric with the mixer, moisture measuring means including a probe positioned in the bottom wall of the mixer in the path of said roller and scraper to have a moist specimen of granular material compressed thereagainst by passage of said roller, said scraper being effective to remove the compressed specimen of moist granular material following each compression thereof against said probe, means responsive to the attainment of a desired moisture content in the granular material operatively connected to said shut-off valve to close the same, timing means having a timing interval slightly longer than the period between successive steps of compressing moist granular material against the probe and operable to re-open said valve if permitted to time out, and means responsive to each compression of granular material and the accompanying measurement of the moisture content of the compressed specimen of granular material which indicates sufiicient moisture content effective to re-start said timing means, whereby said timing means is continuously reset and prevents re-opening of the water shut-off valve so long as successive readings of moisture content indicate a sufficient moisture content.

14. Apparatus as defined in claim 13 which comprises additional timing means whose operation is initiated in response to first sensing of a final desired moisture content and operable when timing out to terminate a cycle and close the said shut-off valve irrespective of the condition of the granular material.

15. Tempering apparatus comprising a container, spaced electrode means in said container, means in said container to compress a specimen of material in the container against said electrode means and to thereafter remove the compressed specimen at regular short intervals, means for adding liquid to the container comprising a shut-off valve, a moisture measuring circuit including said electrode means operable to obtain peak readings when specimens are compressed against said electrode means, means actuated by said circuit to close said shutoif valve upon first sensing by said circuit of a predetermined moisture content, and means to retest the moisture content of material in said container subsequent to closure of said shut-01f valve and to open said shut-E valve only if inadequate moisture content is sensed.

16. Apparatus as defined in claim 15 in which said last recited means includes a timer operated to reopen said shut-off valve if allowed to time out, said timer having a timing interval in excess of the interval between consecutive compressions of specimens against said electrode means, and means operated by each sensing of adequate moisture following initial closure of said shutofi valve to reset said timer to zero.

17. Apparatus as defined in claim 16 which comprises a second timer effective to close said shut-01f valve after a=predetermined interval irrespective of the condition of the material. i

18. Apparatus for tempering granular material which comprises a mixer including means therein for mixing granular material and liquid, liquid addition means for adding liquid directly to said mixer during operation thereof, said liquid addition means comprising a shut-off valve, moisture measuring means for measuring the increasing moisture content of granular material in the mixer during operation thereof and addition of liquid thereto, means operatively connected to said moisture measuring means and to said valve to close said valve to terminate addition of liquid to said mixer upon attainment of a desired moisture content in said granular material, control means for said mixer to eifect continued operation thereof after closure of said valve, and recycling means including a timer operable a predetermined interval after initial liquid addition effective to measure the moisture content of the granular material and to reopen said valve while the measured moisture content is below the desired value and to continue liquid addition until the appropriate moisture content is measured for a second time to avoid inadvertent final valve closure by measurement of appropriate moisture content in a small sample of granular material while its average moisture content is deficient, said recycling means being operative to effect final valve closure upon a later measurement of appropriate moisture content.

19. Apparatus for tempering granular material which comprises a mixer including means therein for mixing granular material and liquid, liquid addition means for adding liquid directly to said mixer during operation thereof, said liquid addition means comprising a first point valve and an end point valve, moisture measuring means for measuring the increasing moisture content of granular material in the mixer during operation thereof and addition of liquid thereto, means operatively connected to said moisture measuring means and to said valves to close said first point valve upon attainment of moisture content near to but below the final required moisture content and to close said end point valve upon attainment of a final required moisture content i said granular material, control means for said mixer to effect continued operation thereof after closure of said valves, and timing means operable a predetermined interval after initial liquid addition effective to condition said apparatus for reopening of both of said valves and continued liquid addition until the appropriate moisture content is measured for a second time to avoid inadvertent final valve closure by measurement of appropriate moisture content in a small sample of granular material While its average moisture content is deficient, said measuring means being operative to effect final valve closure upon a later measurement of appropriate moisture content.

20. Apparatus for tempering granular material which comprises a mixer including means therein for mixing granular material and liquid, liquid addition means for adding liquid directly to said mixer during operation thereof, said liquid addition means comprising a shutoff valve, moisture measuring means for measuring the increasing moisture content of granular, material in the mixer during operation thereof and addition of liquid thereto, means operatively connected to said moisture measuring means and to said valve to close said valve to terminate addition of liquid to said mixer upon attain ment of a required moisture content in said granular material, control means for said mixer to effect continued operation thereof after closure of said valve, and retest means for measuring the moisture content of the granular material following valve closure and operable to reopen said valve if the measured moisture content of said granular material falls below the appropriate valu during continued mixing.

21. Apparatus as defined in claim 20 in which the moisture measuring means operates at short intervals,-

and in which the retest means includes the moisture measuring means and an interval timer having an interval longer than the measuring interval, means connecting said interval timer to said valve to reopen said valve if said interval timer times out, and means connecting said moisture measuring means to said interval timer to reset said interval timer to Zero upon each measurement by said moisture measuring means of appropriate moisture content for the measured temperature of the granular material.

22. Apparatus as defined in claim 21 which comprises additional timing means, means for starting said additional timing means simultaneously with first closure of said end point valve, said additional timing means comprising means for preventing further reopening of said end point valve to finally terminate a tempering cycle.

23. Apparatus for tempering a granular material, which comprises a mixer for receiving the granular material having mixing means therein, liquid supply means including an electrically actuated end point valve for supply liquid directly to the granular material in said mixer during operation of the mixing means, a cycle control system comprising moisture measuring means for measuring the moisture content of the granular material in the mixer during addition of liquid thereto and continued mixing thereof, and a plurality of relays operable in a predetermined sequence from a cycle start position, connections between said measuring means, said relays and said electrically actuated valve operable to close said valve when said measuring means senses a desired moisture content, recycling means connected to said control system and operable to reset said relays to cycle start position, and timing means connected to said recycling means operable to actuate said recycling means a predetermined interval after first initiation of a cycle, to eliminate the eifect of a false moisture measurement due to a wet spot in the granular material.

References Cited in the file of this patent UNITED STATES PATENTS 2,219,497 Stevens et a1. Oct. 29, 1940 2,277,953 Christensen Mar. 31, 1942 2,570,223 Everett et a1. Oct. 9, 1951 2,692,972 Bdgerton et a1. Oct. 26, 1954 2,707,703 Dorst May 3, 1955 2,709,843 Hartley June 7, 1955 2,802,178 Shafer et al. Aug. 6, 1957 2,863,191 Dietert et a1. Dec, 9, 1958 FOREIGN PATENTS 621,181 Great Britain Apr. 5, 1949 

